The term "septal defect" generally refers to a perforation or other type hole (i.e., a defect) which passes through a thin wall of muscle or other tissue (i.e., a septum) which divides or separates "areas" within the body. Such defects can occur, either congenitally or by acquisition, between chambers of the heart (i.e., atrium or ventricle) or the great vessels (interatrial and interventricular septal defects or patent ductus arteriosus and aortico-pulminatry window respectively), causing shunting of blood through the opening.
In the case of the atrium, the presence of a significantly large septal defect can cause blood to shunt across the defect from the right atrium to the left atrium and hence on to the left ventricle, aorta and brain. If the defect is not closed, the risk of stroke is increased.
Shunting of blood from the left to the right side can also have negative consequences. This can lead to death due to cardiac failure or hemoptysis.
In patients with significant sized ventricular septal defects or patent ductus arteriosus, there is shunting of blood from the high pressure left ventricle or aorta, into the right side chambers and pulmonary arteries which normally have much lower pressures. The torrential increase in flow at a high pressure can lead to cardiac failure and death, apart from the serious long-term complication of high pulmonary pressures which can cause a reversal of the direction of the shunt.
Atrial septal defects were initially corrected by open heart surgery which required the surgeon to open the chest of a patient and bypass the heart temporarily (e.g., by means of a mechanical heart or a "heart-lung machine"). The surgeon would then physically cut into the heart and suture small defects closed. In the case of larger defects, a patch of a biologically compatible material would be sewn onto the septum to cover (i.e., "patch") the defect.
In order to avoid the morbidity, mortality and long recovery times associated with open heart surgery, a variety of transcatheter closure techniques have been attempted. In such techniques, an occluding device is delivered through a catheter to the septal defect site. Once the closure device is positioned adjacent the defect, it must be attached to the rest of the septum in a manner which permits it to effectively block the passage of blood through the defect.
One such closure device, as illustrated in U.S. Pat. No. 3,874,388 (King et al.), includes a pair of complex mechanical umbrellas, each having a plurality of arms extending radially from a central hub. The hubs of the two umbrellas are mechanically connected to one another and each umbrella includes a fabric covering over the arms, much like a common umbrella. The ends of each arm are provided with barbs which are anchored into the septum to hold the occluder in place. The complex umbrellas prove rather difficult to unfold after passage through a catheter, requiring an array of cables to deploy the arms. This makes proper placement of the device difficult, and the barbs on the arms prevent retraction or repositioning of the device once it is in place. Use of this device has been limited to adult patients because the device requires a large catheter, such as about 23 French (7.3 mm), for delivery.
Rashkind proposed a single-umbrella closure device capable of delivery through a 5 mm system which permitted use in children weighing at least about 20 kg. Similar to the King device, this umbrella utilizes barbed hooks on the ends of umbrella arms to ensure attachment to the septum, with the single umbrella being placed on the left side of the atrial septal defect. The barbs prevent disengagement of the device, and poorly centered or seated devices requiring open heart surgery for correction are common.
Due to the low success rate of previous devices, a "modified double-umbrella Rashkind occluder" in which the arms of the device are hinged to permit them to fold back against themselves was developed. A more compact collapsed condition and a less intrusive delivery as by an 11 French (3.7 mm) catheter were thereby facilitated. Furthermore, such a "clamshell" occluder did not include barbs at the end of the radial arms of the umbrella, allowing it to be readjusted and retrieved. Typically, this could be accomplished only once, and without subsequent redeployment due to damage or destruction of the device. Although arguably an improvement over heretofore known devices, such a device generally requires a complex loading jig for deployment and remains susceptible to moderately high shunting.
Sideris, in U.S. Pat. No. 4,917,089, proposed an occlusion device which combines a single umbrella with a separate anchoring device. Like the previous defect occlusion devices, Sideris' invention utilizes an umbrella with a plurality of radially extending arms. A string connects the arms of this umbrella to a generally rhomboidally shaped anchor which includes an internal wire skeleton and a central, rhomboidally shaped piece of rubber. The string attached to the struts of the umbrella is affixed to the central rubber element of the anchor. The anchor is placed on the opposite side of the septum from the umbrella, and the length of the string limits movement of the occlusion device with respect to the septum. This style of occluder is difficult to deploy, and its overall bulkiness in the heart causes potential clot emboli due to protrusion into the atrial cavities.
Kotula et al., U.S. Pat. No. 5,725,552, provides a collapsible device comprising a heat-set woven metal fabric configured as a bell, hourglass, etc. for occluding an abnormal opening in a body organ. The device of Kotula et al. does not adequately "fill" the defect nor fit flat against, or readily conform to, the structures within the heart, thereby increasing the embolization potential with the use of such device.
Das, U.S. Pat. No. 5,334,217, teaches an occluder having paired disks, each of which comprises a membrane, and an elastically deformable frame carried about the periphery of each membrane. The disks are joined only at central portions of each membrane, thereby defining a conjoint disk. The Das device is intended to be self-centering within the defect. Since the ability to achieve defect conformity is limited due to the defined conjoint disk structure, residual shunting can occur. Furthermore, with such a device, the conjoint disk cannot uniformly apply and distribute a force to the "second" disk (e.g., as when the second disk follows the first disk into the catheter for purposes of retrieval. As a result, the occluder is caused to contort, resulting in non-symmetrical collapse, and the problems associated therewith.
All of the prior art devices described above suffer shortcomings. First, most of these systems (i.e., the occluder and delivery means) are mechanically complex and require a great deal of remote manipulation for deployment or retrieval, if the device is retrievable. This extensive remote manipulation, such as by applying tension to one or more cables in order to deploy the arms of an umbrella or to anchor the device in place, not only increases the difficulty of the procedure, but tends to increase the likelihood that the device will be improperly deployed. This can necessitate either retrieval, or repositioning so as to effectively occlude the defect and minimize the risk of embolization.
Second, all of these devices, except for Kotula and Das, essentially teach two separate members joined to each other at a single interface. With such device, when the left atrial member is opened, the central point tends to ride to the lower margin of the defect. Proper centering of the device is quite difficult, and when a self centering device as disclosed by Das is employed, it is at the cost of defect conformity.
It is desirable, therefore, to provide a simple, collapsible compact closure device which may be delivered through a small catheter. It is also highly advantageous to have such a device which can be readily reversibly deployed and retrieved with a minimum of remote manipulation and applied force. Further, a device which is self-centering and self-occluding, particularly one that possesses a defect conforming variable geometry to fill slit-like defects and patent foramen ovale, and one that can be released while still being tethered to the delivery mechanism to assure proper placement and function prior to release, would be superior to heretofore known devices. This is particularly true in view of the need to test for shunting of blood around the occluder device prior to release.